Hi xfarmer,
I’m certainly happy to share some information and suggestions that may be helpful but it will be more general in nature than specific because I can’t feel what you feel and there are too many unknowns and variables involved and I don’t have enough specific information or reference points about mattresses you have tried to know the types of fine tuning or changes that would be most effective for you with any certainty.
Jacob is right that firmer isn’t always better and doesn’t necessarily provide better support because it will depend on whether you are trying to change primary support (which is usually about the deeper layers), secondary support (which is usually about the thickness and softness of the comfort layers) or pressure relief. While firming up the base layers can provide firmer primary support under the heavier parts of the body (such as the hips/pelvis), using comfort layers that are too firm can provide poor secondary support under the more recessed parts of the body because you won’t sink in deeply enough to “fill in” the gaps in your sleeping profile which can also lead to back pain. Don’t forget that you “need” to sink in to some degree to provide “contouring support” under the different parts of the body so you end up with good alignment in all your sleeping positions. There is more about what I call primary and secondary support and their relationship to pressure relief in Post #2 here and post #4 here that may be helpful in understanding what “good support” really means.
There is also more about the most common “symptoms” that people may experience on a mattress and some of the reasons that can contribute to them in post #2 here).
Given your lighter weights … it’s less likely that the firmness of the support core would be an issue and it’s very possible that you may do better with a softer comfort layer that would provide you with better secondary support and pressure relief although only your own sleeping experience will be able to confirm this in “real life”.
There are also some suggestions in post #2 here that may be helpful if you suspect that your mattress is too firm for you and some suggestions in post #4 here that may be helpful if you suspect that your mattress may be too soft.
Phoenix